The purpose of this invention is to describe propellants with a controllable burning rate and a process for preparing them. The propellants comprise a class of nitrocellulose base materials that incorporate a burning rate enhancer chosen from any of three classes of compounds based on decahydrodecaborate salts.
The present invention describes a class of propellants that are useful as gun or rocket propellants and in pyrotechnic devices such as gas generators. In these types of applications, a controlled amount of gas and heat must be released within a specified time period by the burning propellant. With existing propellants based on nitrocellulose, nitrocellulose/nitroglycerine, and nitrocellulose/nitroglycerine/nitroguanidine, and better known to those practiced in the art as "single base," "double base," and "triple base" propellants, respectively, the burning rate of the propellant is fixed within rather narrow limits by the formulation; a major change in propellant formulation is required to significantly alter such characteristics as burning rate. As a result, to control the release of heat and gas in a device such as a rocket motor chamber, gun chamber, or other gas generating device, the propellant is configured into a sometimes complicated three dimensional geometry, known as a "grain," so that the amount of surface burning at a given time is controlled, rather than the actual regressive burning rate of the propellant matrix. In addition, the manufacturing lot-to-lot variations in characteristics such as burning rate are somewhat difficult to control for certain classes of these propellants.
This invention describes propellants in which the burning rate is easily controlled, by the addition of a burning rate catalyst into the propellant matrix. An important feature of the invention is that the burning rate catalyst can be added to numerous existing propellant formulations to derive the subject propellants, with the effect that the range of burning rates available from the manifold of tested and qualified propellants can be greatly enhanced. The method of adding the burning rate catalyst is not critical: it can be added during the manufacturing process, or alternatively, after the nitrocellulose base propellant has been completely processed, or even formed into a grain. The new propellants incorporating the burning rate catalyst into the entire bulk of the propellant to alter the burning characteristics throughout the grain, or by "seeding" the catalyst into a surface layer of an existing grain, so that the grain is effectively coated with a surface layer of the new propellant composition, thereby altering the initial burning rate of the grain.
The end product of the subject invention is a nitrocellulose base propellant that enables the grain designer a much broader range of burning rate options, which can in turn be used simply with existing grains or perform more sophisticated functions with new designs.